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Cisco MGX 8850 (PXM1E/PXM45), Cisco MGX 8950, Cisco MGX 8830, and Cisco MGX 8880 Configuration Guide
Release 5.0.10, OL-3845-01 Rev. B0, August 16, 2004
Chapter 8 Managing PNNI Nodes and PNNI Routing
Managing Connection Grooming
How Grooming Reroutes Connections
Cisco MGX switches use two different reroute methods for grooming connections. Prior to Release 5,
Cisco MGX switches use only the hard reroute method. During a hard reroute, a connection that has been
selected for grooming is disconnected, and then a new connection is built over a new route. The
disadvantage to this approach is that the new connection is not validated before the original connection
is released. Another disadvantage is that even when the new connection is operational, hard rerouting
interrupts connection service for a longer period of time than soft rerouting. The hard reroute method is
sometimes called the break-before-make method.
Soft rerouting is introduced in Release 5 Cisco MGX switches for grooming of P2P connections. During
a soft reroute, a new connection is established and validated before the existing or incumbent connection
is released. When the new connection is ready for use, the switch changes to the new connection with a
momentary interruption of service. When the connection is established on the new connection, the
incumbent connection is released. The soft reroute method is sometimes called the make-before-break
method. Figure 8-2 illustrates how a soft reroute operates.
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